//调用方法
object?.deepProp?.function?.(args)
//数组
object?.deepProp?.deepArray?.[5]
//表达式 知道就行，不要这样用！
object?.deepProp?.[console.log("runs if deepProp defined")]

type Names = "Bob" | "Bill" | "Ben";
type JobTitles = "Welder" | "Carpenter" | "Plumber";

const JobAssignments: { [Key in Names]?: JobTitles } = {
  Bob: "Welder",
  Bill: "Carpenter",
  Ben: "Plumber"
};

function inputDoubler(input: string): string;
function inputDoubler(input: number): number;

function inputDoubler(input: string | number) {
  if (typeof input === "string"){
    return `${input}${input}`;
  } else {
    return input * 2;
  }
};

inputDoubler(5) + inputDoubler(10);

function isPizza (food: Pizza | Burrito): food is Pizza {
  return food.ingredients.topping !== undefined;
};

function printIngredients (food: Pizza | Burrito) {
  if (isPizza(food)) {
    console.log(food.ingredients.topping);
  } else {
    console.log(food.ingredients.filling);
  };
};